-- she'll tell you that Magnus has a cabin up in the hills, and Elisabet has the key to it. And since there's no chance at ALL that Elisabet will give you that key, you're going to have to find a way to distract her so you can loot her purse.
You might trip across the way to do this by accident --
-- but if not, I'll tell you that you need to use the radio in the ship's wheelhouse.
After you finish doing all the chores the person on the radio told you to do, you now know --
-- that there's an alarm in the wheelhouse that Elisabet will run to answer. That alarm is on the side of the chair in the wheelhouse.
After you push the alarm button, leave the wheelhouse and go dig through Elisabet's purse. You'd think you ought to do this as fast as you can -- but in point of fact, I waited a good five minutes and never saw a sign of Elisabet, so you probably don't need to bolt.
In the purse, you'll find a key with a house-shaped keyring; take it. There's also a letter from Magnus that tells you how to solve a puzzle in Magnus's cabin, and you can't take the letter, so take a picture of it for later.